[Experimental comparison of temporal bone imaging protocol optimization between 10 μm otology CT and multi-slice CT]

Objective: To evaluate different protocol optimization strategies for temporal bone between10 μm otology CT and multi-slice CT (MSCT). Methods: Ten adult skull specimens (20-sides temporal bones) were prospectively enrolled. From October to November 2020, the temporal bones were scanned under four different imaging conditions using 10 μm otology CT (90 kV, 120 mAs; 90 kV, 140 mAs; 100 kV, 120 mAs; 100 kV, 140 mAs) and MSCT (120 kV, 220 mAs; 120 kV, 310 mAs; 140 kV, 160 mAs; 140 kV, 220 mAs), respectively. The image quality was subjectively scored using 5-grade scores, and the contrast noise ratio (CNR) of the image was measured. The absorbed dose of tissues and organs under different imaging conditions was measured by thermoluminescence dosimeter, and the effective dose was calculated. The figure of merit (FOM) is defined as the ratio of the square of the mean CNR to the effective dose. χ² test was used to compare the difference of subjective scores of different scanning parameter groups, and paired t test was used to analyze and compare the difference of image CNR of different scanning parameter groups. The image quality, radiation dose and FOM of the combination of recommended parameters of the two devices were analyzed and compared. Results: For 10 μm otology CT, under 100 kV condition, the CNR of 140 mAs group was better than that of 120 mAs group (11.27±1.85 vs 10.26±1.38, P<0.001). There was no significant difference in subjective scores between the two groups [5.00 (4.00, 5.00) vs 5.00 (4.25, 5.00), P=0.264]. For MSCT, under 120 kV condition, the subjective scores and CNR of 310 mAs group were better than those of 220 mAs at 120 kV [4.00(3.00, 4.00) vs 3.00(3.00, 3.00),P=0.002;5.24±0.62 vs 4.60±0.62,P<0.001]. According to the principle of image quality-radiation dose optimization, the combination of 100 kV with 120 mAs and 120 kV with 310 mAs are recommended for 10 μm otology CT and MSCT, respectively. The subjective scores and CNR of 10 μm otology CT images were better than those of MSCT (5.00 (4.25, 5.00) vs 4.00 (3.00, 4.00), 10.26±1.38 vs 5.48±0.22, P<0.001). The effective dose was 1/3 of that of MSCT (82.99 μSv vs 252.56 μSv), and the FOM was 11.16 times of that of MSCT (1 268.44 mSv^-1 vs 113.71 mSv^-1). Conclusion: The temporal bone image quality of newly developed 10 μm otology CT is significantly better than that of MSCT, and its effective dose is lower than that of MSCT, which has more accurate and safer application potential.